Missouri House members have given first-round approval to legislation taking aim at synthetic drugs.

The bill would add several specific substances to what is considered synthetic marijuana.

It was endorsed by a voice vote Tuesday and needs a second vote before moving to the Senate.

In recent years, Missouri has tried to keep pace with evolving synthetic drugs and twice has approved legislation targeting them. Sponsoring House member Shawn Rhoads says the current bill is needed to stay ahead in the effort.

Federal officials and Springfield police say the availability of synthetic drugs in the area has dropped significantly since some shop owners were indicted in December.

Before the indictments, law enforcement had trouble disrupting the synthetic drug trade in Springfield region because the developers could quickly alter the drugs' chemicals just enough to avoid prosecution.

At least a half-dozen people are behind bars in the St. Louis area following a nationwide crackdown on the sale of designer narcotics known as "bath salts" or K2.

The federal Drug Enforcement Agency coordinated the Wednesday operation known as "Log Jam." Overall, nearly 80 people were arrested, and more than 5 million packets of the synthetic drugs seized, along with tons of raw material. It was the first coordinated strike.